Attorney General Eric Holder faced sharp questioning from lawmakers Tuesday about why the Justice Department allowed as many as 2,000 guns in Operation Fast and Furious to flow to Mexico with little control over the weapons and about why the department’s initial statements to Congress were incorrect.

Sen. John Cornyn (R-Texas) demanded to know whether Holder had apologized to the family of murdered U.S. Border Patrol Agent Brian Terry, whose death has been linked to the Fast and Furious operation.

“I have not apologized to them,” said Holder.

Pressed by Cornyn to apologize on the spot, Holder said, “I certainly regret what happened to Agent Terry. I can only imagine the pain that his family has had to deal with, particularly his mother…We are not programmed to bury our kids. It pains me whenever there is the death of a law enforcement official, especially under the circumstances. It is not fair, however, to assume that the mistakes that happened in Fast and Furious directly led to the death of Agent Terry.”

Cornyn also disputed Holder’s description of Fast and Furious, in his opening statement, as “a local law enforcement operation.”

“This is far from, as you stated earlier, a local law enforcement operation as far as its impact,” the Texas Republican said, noting that 119 Fast and Furious weapons have been found at crime scenes in his state.

“That’s my fault,” Holder said. “It’s a federal law enforcement operation that was of local concern. It was not a national operation.”

Under questioning by Sen. Mike Lee (R-Utah), Holder said he could point to no mistake he made in connection with Fast and Furious.

“I think I acted in a responsible way,” the Attorney General said.

A pointed exchange between Cornyn and Holder on the differences between the Bush-era “Wide Receiver” program and “Fast and Furious” led the Senator to remark, “Are you winging this, or do you actually know?”

“Senator, I am not trying to equate the two, I’m not trying to equate ‘Wide Receiver’ and ‘Fast and Furious,’” replied Holder.

Cornyn noted that “Wide Receiver” involved efforts to coordinate with Mexico, while Fast and Furious seems to have been conducted without any such attempt. However, documents show that the Mexicans often failed to interdict or follow the Wide Receiver weapons, perhaps due to corruption.

In his opening remarks at a Senate Judiciary Committee oversight hearing, Holder criticized Republicans for leveling what he called misleading allegations surrounding the Fast and Furious operation.

“I would like to correct some of the inaccurate — and frankly some of the irresponsible — accusations surrounding Fast and Furious,” Holder said. “Some of the overheated rhetoric might lead you to believe that this local, Arizona-based operation was somehow the cause of the epidemic of gun violence in Mexico. In fact, Fast and Furious was a flawed response to, not the cause of, the flow of illegal guns from the United States into Mexico.”

Holder portrayed himself as as mystified as lawmakers about why guns were sent to Mexico with few if any efforts to track their whereabouts. “Like each of you, I want to know why and how firearms that should have been under surveillance could wind up in the hands of the Mexican drug cartels,” Holder said.

“I don’t know the answer to…who actually thought that this was a good thing to do,” Holder added later.

In his opening remarks, Senate Judiciary Ranking Member Chuck Grassley (R-Iowa) slammed the Justice Department for its “utter failure to enforce our existing gun laws in Fast and Furious.”

“The bottom line is that it doesn’t matter how many laws we pass if those responsible for enforcing them refuse to do their duty—as was the case in Fast and Furious,” Grassley said.

A particular target of GOP criticism was the chief of the Justice Department’s Criminal Division, Lanny Breuer. Grassley faulted Breuer for allowing the department to send a letter to Congress in February denying that the Bureau of Alcohol, Tobacco, Firearms and Explosives engaged in a tactic known as gunwalking, where weapons law enforcement agents had authority to intercept are allowed to flow into criminal networks.

Breuer “was aware that Congress had been misled but made no effort to correct the department’s official denial,” Grassley complained. “It was Mr. Breuer’s responsibility to clearly communicate that gunwalking was not acceptable and to insitutute oversight and safeguards to ensure that it did not happen again. He did not do that….The government should have stopped the flow of guns to these criminals.”

Breuer has acknowledged he was briefed on a Bush-era operation that used similar tactics and has said he regrets not pursuing the issue, particularly after Fast and Furious drew public attention.

Grassley stopped short of calling for Breuer’s firing, but the Iowa Republican said: “I am eager to hear from the attorney general who he plans to hold accountable.”

Under questioning by Grassley, Holder said Breuer has not offered his resignation. “No, he has not and I do not expect to hear a resignation offer.”

Lee argued that Breuer’s deputies should have known about the details of Fast and Furious because they approved several wiretap applications for the operation. “They have to undertake an assessment of have other investigative tactics proven insufficient,” Lee noted.

Holder said he hasn’t read those applications, but doubts they went into detail about gunwalking. “I don’t have any information to indicate [the wiretap applications] talked about the tactics that have made this such a bone of contention,” the attorney general said. “I’d be surprised if the tactics themselves, about gunwalking, were actually contained in those applications.”

Holder conceded the February letter denying ATF was involved in gunwalking was wrong, but he suggested those involved were acting in good faith. “There was information in that letter that was inaccurate. The letter could have been better crafted,” the attorney general said. “I regret that.”

“People were relying on information provided to them by people we thought were in the best position to know what was accurate,” including officials from the ATF and the U.S. Attorney’s Office in Arizona, Holder said.

Not all Judiciary Committee Republicans pursued questioning on the topic of Fast and Furious, as Sens. Orrin Hatch of Utah and Lindsey Graham of South Carolina pursued other topics.

Meanwhile, Democratic senators including committee chairman Patrick Leahy of Vermont, Dianne Feinstein of California and Chuck Schumer of New York tried to push the focus onto Bush-era gunwalking, including that during the 2006-2007 “Wide Receiver” operation.

Leahy seemed to regard the Fast and Furious questioning with some disdain. As he excused Holder, Leahy said the attorney general could now return to “issues that really matter.”

Holder has been under fire because Republicans question whether he lied in previous in previous testimony in front of the House about when he first heard of the Fast and Furious operation; dozens of Republicans have called for his resignation.

On May 3, Rep. Darrell Issa (R-Calif.) asked when Holder had first learned of the program, to which Holder replied, “I probably heard about Fast and Furious for the first time over the last few weeks.”

A July 2010 memo addressed to the Attorney General mentions the Fast and Furious Operation, which Republicans say means that Holder lied in his testimony.

Holder said those memos were never put in front of him.

“These reports are prepared with my name on them… they are reviewed by my staff and a determination made as to what should be brought to my attention,” said Holder. “If you look at those memos, there’s nothing in those memos that indicates any of those inappropriate tactics that are of concern to us now… and my staff made a determination that there was no reasons to share.”

Holder said that he first learned of the tactics used in the Fast and Furious operation earlier this year, when it became a matter of controversy.

“I did say ‘a few weeks’, I probably could have said, a couple of months….I don’t think my using the term a few weeks was inaccurate based on what happened,” said Holder in testimony today, who said this wasn’t an attempt to mislead Congress. “The focus of which day and which month is a bit of a distraction.”

Holder said that he was “bothered by it, offended by it” when he first heard of the tactics used.

The attorney general seemed upset and taken aback when Grassley said in the course of questioning that Holder had disciplined a Justice Department employee for leaking information intended to discredit an ATF agent who blew the whistle on the gunwalking aspect of Operation Fast and Furious.

“It almost pains me,” Holder said of Grassley’s disclosure of what the attorney general called a “private conversation.”

“I called you to try to indicate to you that I had taken that matter seriously,” Holder said. “In a different time in Washington, I’m not sure what you just said would have been shared with everyone here,” Holder said, adding wistfully, “It’s a different time.”

Aides to Grassley said they repeatedly pressed the Justice Department for information about who had been disciplined or was being investigated for Fast and Furious-related leaks, but got conflicting and sketchy answers from the department. At least one person appears to have resigned after being linked to disclosures about undercover work by an ATF agent who testified in June before a House committee probing Fast and Furious.

During questioning, Holder said that those who made mistakes during Fast and Furious would be held accountable for their actions.

“I will assure you and the American people that we will people will be held accountable for any mistakes that were made in Fast and Furious,” Holder said.

In his opening remarks, Holder also warned that the effects of Operation Fast and Furious would not be going away anytime soon.

“Unfortunately, we will feel its effects for years to come as guns that were lost during this operation continue to show up at [crime] scenes both here and in Mexico,” he said. “This should never have happened. And it must never happen again.”

The Attorney General is expected to testify again on Dec. 8 in front of the House Judiciary Committee.

The Fast and Furious probe attempted to investigate drug cartels and weapons traffickers but instead ended up supplying them with weapons. Investigators lost thousands of firearms, many of which crossed the border into Mexico.

Fast and Furious operation drew intense scrutiny when firearms linked to the program were found to be involved in the December 2010 shooting death of U.S. Border Patrol Agent Brian Terry.